Hellknight is a good option for a lawful evil heavilly armored character.
We have not and have no plans to update the blackguard prestige class, though; our take on the fallen paladin is instead the antipaladin archetype. We knew some folks would end up preferring the blackguard prestige class as a solution to that, though, which is why we didn't call ours a "blackguard" but instead called it an antipaladin. Even though we have no plans to update the blackguard or do anything with it in Pathfinder, we didn't want to "use up" the name for something drastically different than what it was used as in 3.5, so that folks could just use the 3.5 rules for the prestige class (after making the appropriate adjustments to its saving throw progression) as-is in their Pathfinder games.